The TTL logic limits are 4.75V - 5.25V. So you are out of specs.

There are many reasons for that. Check your ground connections, and especially that the voltage regulator mounting screws at the driver board heat sink are tight.

Yes it is too high and a fairly chronic condition in these old bally/stern games. They juice up the regulator output and I have wondered if it contributes to MPU IC failure, specially the stressed out U15 chip and others like the complete oscillators on my replacement MPU. I have seen some come in at 5.6- 5.8vdc. A lot of people probably never check it and its been like that for years.

On the SDB cut out R49 and recheck voltage. If it is still not under 5.25vdc jumper over top of R50. That should bring you down into good range.
Untitled (resized).png

Thanks barakandl! I did not remember Bally used those resistors on voltager regulator, and just thought that if the regulator does not have a solid ground connection it will rise the output voltage.

But as said, I would definitely cut out R49 and short R50. The regulator then gives out 5.0 volts - enough for everything. Cranking the regulator for more output is not a proper way to handle voltage loss at bad connectors.

It is still a bit on the high side. I would replace the regulator.

Resistors R49 and R50 are there to bump up the output voltage a little to presumably account for voltage losses in connectors.

Assume the LM323 outputs a perfect 5.00 volts between its pin 2 and 3, R50 and R49 increases the output voltage with this simplified equation:
Vout = 5.00 * (1+ (R2/R1))
Vout = 5.00 * (1 + (R50 / R49))

Bally and Stern use a 100 ohm resistor at R49.
Bally uses a 2.2 ohm resistor at R50
Stern uses a 4.7 ohm resistor at R50

Therefore a Bally board based on the above formula will output around 5.11 volts
A Stern board based on the above formula will output around 5.23 volts

Tolerance on the LM323K is 5% so some parts will output 5.25 volts.
Using Sterns resistors, with a LM323K outputting max 5.25 volts and the above equation gives us a total output of 5.49 volts.

Measure the 5V rail on the MPU board, you'll probably find it's a little lower than the solenoid driver board.

barakandl Quench I've added the LM323 voltage adjust info to the PinWiki, betting that Andrew wouldn't mind me using the image in this thread.
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Chris Hibler - CARGPB #31
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that is fine.

I am guessing when R50 starts to burn is when the voltage creeps up towards 6vdc. It happens on the Bally boards too.

Argh, it might help if I refer to the resistor numbers in this circuit instead of the datasheets. So in this case the formula is:

Vout = 5.00 * (1 + (R50 / R49))

Thanks Chris, can you update the formula on PinWiki?

Do you want to test the LM323 on the solenoid driver board or as a loose component?

Hook up ground to the LM323 casing and the 12V wire to the input leg as per below. You should measure 5 volts between the casing and the output pin.
However this tests it without a load and generally fake Chinese parts will pass this test.
A fake part I was testing a few years ago shutdown when I put a load drawing somewhere around 1.4 amps from memory. I suspect they are really 1.0 amp parts.

I use high watt, low ohm resistors as a load. You could probably use a couple of #44 incandescent lamps in parallel. They're usually rated to 0.3 amps at 6.3 volts. At 5 volts they'll probably draw around 0.24 amps.
The LM323 is spec'd to deliver a maximum of 3.0 amps continuous (on a heatsink).

LM323K_pinout.png

Yep. I was going to update that anyway.
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Chris Hibler - CARGPB #31
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That is true. However, the true check should be at the vcc on the ttl chips themselves. The test points in most games (vids/pins) are usually always high because they are taken at the source under no load or voltage/cable drop. They are there as a quick raw measurement.

You really need to measure the 5v at the components that need 5v to run, (ttl, etc) then determine if its in the range for that chip to operate in this case 4.75-5.25v. In the end it is that voltage that really matters.

Often times the number will be significantly lower depending on drop/distance, traces etc.